The British Royal Navy, as of 2005, will require all officers and sailors to pass a physical fitness test before they can be promoted. This sort of thing has come and gone many times over the last century. For thousands of years, sailors being out of shape was a non-issue. So much physical activity was required to operate a sailing ship that, by definition, a sailor was in shape. It was a different story for officers, especially senior ones. And many of these fellows were overweight or otherwise physically impaired. But they were there to give orders, not carry them out. As long as their brain muscle worked, all was well. However, by early in the 20th century, all military ships were powered by engines, not sail, and sailors didnt have to be so buff to get their job done. Over the decades, less physical effort, and more food, led to larger, and less physically fit, sailors.
It was always recognized that being in good physical shape, in general, made for a more capable sailor, soldier, airman, marine or whatever. But except in those jobs that still clearly called for being in top shape (infantry, for example), the attitude tended to be, if he gets his job done and doesnt look too bad in formation, so what. However, service commanders would come along from time to time, especially when the recruiters were bringing in all the people needed, and decree that you had to be physically fit to get promoted, or even stay in the service.
The Royal Navy will make exceptions for medical problems and for the needs of the service (meaning they desperately need the out-of-shape sailor and are willing to overlook his poor pushup skills). The medical exception angle usually leads to a lot of creative efforts by sailors to suddenly develop cronic and incurable conditions that do not prevent them from doing their jobs, but do, alas, make it impossible to pass the physical fitness test. While all this physical fitness stuff is done with the best of intentions, human nature usually prevails in the end.